Sanitize and modernize pytests

Some of these tests were written before some of our convenient
tooling existed. Additionally, some of the tests were not
cooperating with PEP-8 guidelines or isorted.

This commit does the following:
    - Replaces all calls to make_(user|session) with
      aurweb.db.create(Model, ...).
    - Replace calls to session.add(...) + session.commit() with
      aurweb.db.create.
    - Removes the majority of calls to (session|aurweb.db).delete(...).
    - Replaces session.query calls with aurweb.db.query.
    - Initializes all mutable globals in pytest fixture setup().
    - Makes mutable global declarations more concise:
      `var1, var2 = None, None` -> `var1 = var2 = None`
    - Defines a warning exclusion for test/test_ssh_pub_key.py.
    - Removes the aurweb.testing.models module.
    - Removes some useless pytest.fixture yielding.

As of this commit, developers should use the following guidelines
when writing tests:
    - Always use aurweb.db.(create|delete|query) for database
      operations, where possible.
    - Always define mutable globals in the style: `var1 = var2 = None`.
    - `yield` the most dependent model in pytest setup fixture **iff**
      you must delete records after test runs to maintain database
      integrity. Example: test/test_account_type.py.

This all makes the test code look and behave much cleaner.
Previously, aurweb.testing.setup_test_db was buggy and leaving
objects around in SQLAlchemy's IdentityMap.

Signed-off-by: Kevin Morris <kevr@0cost.org>

test/test_accepted_term.py

@@ -2,14 +2,14 @@ import pytest
 
 from sqlalchemy.exc import IntegrityError
 
-from aurweb.db import create, delete, query
+from aurweb.db import create, query
 from aurweb.models.accepted_term import AcceptedTerm
 from aurweb.models.account_type import AccountType
 from aurweb.models.term import Term
 from aurweb.models.user import User
 from aurweb.testing import setup_test_db
 
-user, term, accepted_term = None, None, None
+user = term = accepted_term = None
 
 
 @pytest.fixture(autouse=True)
@@ -26,11 +26,6 @@ def setup():
 
     term = create(Term, Description="Test term", URL="https://test.term")
 
-    yield term
-
-    delete(Term, Term.ID == term.ID)
-    delete(User, User.ID == user.ID)
-
 
 def test_accepted_term():
     accepted_term = create(AcceptedTerm, User=user, Term=term)
@@ -40,8 +35,6 @@ def test_accepted_term():
     assert accepted_term in user.accepted_terms
     assert accepted_term in term.accepted
 
-    delete(AcceptedTerm, AcceptedTerm.User == user, AcceptedTerm.Term == term)
-
 
 def test_accepted_term_null_user_raises_exception():
     from aurweb.db import session